In this art, U.S. Pat. No. 5,079,496 discloses a regulator device which comprises a regulator circuit acting on the mean value of the rectified alternator voltage and including in succession a circuit for obtaining the mean value, a threshold comparator, a timing circuit, and a power stage for controlling the current flowing through the excitation winding of the alternator.
In such a prior circuit, the circuit for obtaining the mean value is constituted by envelope detector based on the positive peaks of the voltage to be regulated, and associated with an RC filter having the free end of its capacitor connected to the output of said detector. The purpose of such a circuit is to obtain the mean value of the voltage to be regulated while introducing hardly any phase shift or delay, so as to avoid encouraging an excessive drop in the frequency at which regulation is performed. It is recalled that such a drop in frequency is harmful, in particular since it makes the driver aware of variations in the intensity of the light beams produced by the vehicle headlights.
That prior circuit is easy to implement using discrete electronic components, but presents difficulties when it is to be implemented in monolithic technology. More particularly, that circuit requires capacitance in the envelope detector that is expensive in silicon area. This gives rise to a product of increased cost and size.
The present invention seeks to mitigate this drawback of the prior art and to propose a device that can easily be integrated on a silicon chip.
An auxiliary object of the invention is to propose a regulator device which increases the frequency at which regulation takes place reliably and significantly under limiting operating conditions.